In UMTS (Universal Mobile Telecommunications System) networks, for the purpose of improving spectral efficiency and further improving data rates, by adopting HSDPA (High-Speed Downlink Packet Access) and HSUPA (High Speed Uplink Packet Access), it is performed exploiting maximum features of the system based on W-CDMA (Wideband Code Division Multiple Access). For the UMTS network, for the purpose of further increasing high-speed data rates, providing low delay and the like, Long Term Evolution (LTE) has been studied (Non-patent Literature 1).
In the 3G system, a fixed band of 5 MHz is substantially used, and it is possible to achieve transmission rates of approximately maximum 2 Mbps in downlink. Meanwhile, in the LTE system, using variable bands ranging from 1.4 MHz to 20 MHz, it is possible to achieve transmission rates of maximum 300 Mbps in downlink and about 75 Mbps in uplink. Further, in the UMTS network, for the purpose of further increasing the wide-band and high speed, successor systems to LTE have been studied (for example, also called LTE Advanced (LTE-A) or LTE Enhancement).
In such a system, as a duplex scheme applied to radio systems, there are a Frequency Division Duplex (FDD) scheme and Time Division Duplex (TDD) scheme. In the FDD scheme, different frequency bands spaced a sufficient interval are used in uplink and downlink. In the TDD scheme, the same frequency band is used in uplink and downlink, and uplink communications and downlink communications are divided by time. In the FDD scheme, it is necessary to adequately widen the interval between the frequency bands used in uplink and downlink, and therefore, not only the base station apparatus but also the mobile terminal apparatus require a duplexer with high accuracy.
Further, mobile terminal apparatuses (Rel. 8 or later) of LTE system and its successor system support also a Half-duplex FDD scheme. In the Half-duplex FDD scheme, as in the FDD scheme, different frequency bands are used in uplink and downlink, while uplink communications and downlink communications are switched by time. Therefore, mobile terminal apparatuses do not need a duplexer with high accuracy, and it is possible to simplify the mobile terminal apparatuses.